Axial field rotary energy device with PCB stator panel having thermally conductive layer

ABSTRACT

An axial field rotary energy device has a PCB stator panel assembly between rotors with an axis of rotation. Each rotor has a magnet. The PCB stator panel assembly includes PCB panels. Each PCB panel can have layers, and each layer can have conductive coils. The PCB stator panel assembly can have a thermally conductive layer that extends from an inner diameter portion to an outer diameter portion thereof.

This application claims priority to and the benefit of U.S. Prov. App.No. 62/933,598, filed Nov. 11, 2019, U.S. Prov. App. No. 62/933,795,filed Nov. 11, 2019, and U.S. Prov. App. No. 62/960,769, filed Jan. 14,2020, each of which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present invention relates in general to an axial field rotary energydevice and, in particular, to a system, method and apparatus for motorsand generators having one or more printed circuit board (PCB) stators.

BACKGROUND

Some axial field electric machines, such as motors or generators, useprinted circuit board (PCB) stator structures. Examples of such devicesare described in U.S. Pat. Nos. 10,141,803, 10,135,310, 10,340,760,10,141,804 and 10,186,922. Although those designs are workable,improvements continue to be of interest.

SUMMARY

Embodiments of an axial field rotary energy device with a PCB statorpanel having thermally conductive layers are disclosed. For example, thedevice can include rotors having an axis of rotation. Each rotorcomprises a magnet. The device can further include a stator assemblylocated axially between the rotors. The stator assembly can includeprinted circuit board (PCB) panels. Each PCB panel can have layers, andeach layer can have conductive coils. The stator assembly can have athermally conductive layer that extends from an inner diameter portionto an outer diameter portion of the stator assembly.

The foregoing and other objects and advantages of these embodiments willbe apparent to those of ordinary skill in the art in view of thefollowing detailed description, taken in conjunction with the appendedclaims and the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the features and advantages of theembodiments are attained and can be understood in more detail, a moreparticular description can be had by reference to the embodiments thatare illustrated in the appended drawings. However, the drawingsillustrate only some embodiments and are not to be considered limitingin scope since there can be other equally effective embodiments.

It shall be noted that some of the details and/or features shown in thedrawings herein may not be drawn to scale for clarity purposes.

FIG. 1 is a front or axial view of an axial field rotary energy device.

FIG. 2 is a sectional side view of the device in FIG.1, taken alongsection line A-A.

FIG. 3A is a front or axial view of a PCB stator.

FIG. 3B is a front or axial view of a segmented PCB stator.

FIG. 4 is a schematic sectional side view of a device with two magneticrotors and a 3-phase PCB stator with magnetic flux lines crossingbetween the rotors through the PCB stator.

FIG. 5 is a schematic sectional side view of an embodiment of an axialfield rotary device having two magnetic rotors and a 3-phase interleavedPCB stator depicting magnetic flux lines crossing between the rotors andthrough the PCB stator.

FIG. 6 is an enlarged, partial, sectional side view of an embodiment ofthe PCB stator of FIG. 5.

FIG. 7A is a schematic diagram of an embodiment of layers of a PCBstator depicting coils with different numbers of turns in differentlayers.

FIG. 7B is a schematic diagram of an embodiment of layers of a PCBstator depicting coils with different number of turns in the same layer.

FIG. 8 is a schematic view of a single coil of a PCB stator relative tothe magnetic field active area produced by the rotor magnet.

FIG. 9 is a schematic view of an embodiment of a single coil of a PCBstator relative to the magnetic field active area produced by the rotormagnet, showing the coil conductors in a serrated pattern.

FIG. 10 is a schematic view of another embodiment of a single coil of aPCB stator relative to the magnetic field active area produced by therotor magnet, showing the coil conductors in a square wave pattern.

FIG. 11 is a schematic sectional side view of a portion of a PCB statormounted to a machine housing, showing a heat flow scheme.

FIG. 12 is a schematic sectional side view of an embodiment of a PCBstator showing thermally conductive layers and other heat removalfeatures included with the device.

FIG. 13 is a partial perspective view of the embodiment of FIG. 12.

FIG. 14 is a schematic sectional view of an alternate embodiment of adevice showing external and internal thermally conductive layers andother heat removal features included with the device.

FIG. 15A is a schematic sectional side view of an alternate embodimentof a device with multiple external and internal thermally conductivelayers.

FIG. 15B is a schematic sectional side view of another alternateembodiment of a device with multiple external and internal thermallyconductive layers.

FIG. 16 is a partial axial view of an embodiment of a PCB stator with athermally conductive layer having substantially straight traces orientedradially relative to the PCB stator.

FIG. 17 is an enlarged view of a portion of the embodiment of FIG. 16.

FIG. 18 is a partial axial view of an embodiment of a PCB stator with athermally conductive layer having non-linear traces.

FIG. 19 is an enlarged view of a portion of the embodiment of FIG. 18.

FIG. 20 is an axial view of an embodiment of a PCB stator with athermally conductive layer having sectioned traces.

FIG. 21 is an enlarged view of a portion of the embodiment of FIG. 19.

FIGS. 22A and 22B are axial views of an embodiment having some tracesinterconnected to form a voltage sensor.

FIGS. 23A and 23B are sectional side and axial views, respectively, of aportion of an embodiment where the PCB stator is clamped between housingsections.

The use of the same reference symbols in different drawings indicatessimilar or identical items.

DETAILED DESCRIPTION

Some axial field electric machines can include one or more PCB stators,such as one for each electrical phase of the machine. FIGS. 1 and 2depict an example of an axial field rotary energy device, such asmultiphase device 100. The multiphase device 100 can include at leastone rotor 110 with an axis 120 of rotation. Each rotor can comprise atleast one magnet 130. The multiphase device 100 also can include atleast one PCB stator 200.

As shown in FIG. 3A, each PCB stator 200 can include a plurality ofcoils 210 formed, for example, in the copper laminated structure of thePCB. The coils 210 can include multiple turns depending on the design ofthe stator. The coils 210 in the PCB stator 200 can be interconnectedwith traces (not shown in FIG. 3A) located in the PCB copper laminatestructure to form north and south magnetic poles. Although FIG. 3a showsan example of a 32-pole stator, many other pole configurations arepossible.

In FIG. 3A, the circular disk example of PCB stator 200 depicts eachcoil with 3 turns. Each turn can include, for example, two straightsections 220 of conductors that are substantially radially oriented withrespect to the axis 120 (FIG. 2). The straight sections 220 can beconnected by arches or arch traces or segments 230, which can extendcircumferentially relative to the axis 120.

In alternate embodiments, the PCB stator 200 can be segmented intoseparate PCB pieces or components that are coupled together to form asingle stator. FIG. 3B depicts an example of the PCB stator 200 withfour annular PCB segments 200A, 200B, 200C and 200d, each of which hasits own set of coils 210. Although FIG. 3b has a four-segment PCB stator200, other embodiments can have a different number of segments such astwo, three, six, etc.

In the multiphase device 100, the voltages induced in each phase may notbe symmetrical due to non-uniform flux distribution across the PCBstator 200. FIG. 4 shows an example of a multiphase device 100comprising two rotors 110. Each rotor 110 can have a plurality ofmagnets 130 arranged to produce a magnetic flux 140 across an air gap150 between the rotors 110. In this version, the PCB stator 200 hasthree PCB panels 200 a, 200 b and 200 c, each having coils for adifferent electrical phase. The voltage induced in the phase carried bypanel 200 b can be lower than the voltages induced in phases carried bypanels 200 a and 200 c, since there are fewer magnetic flux lines linkedwith the panel 200 b.

FIG. 5 depicts an embodiment of the device 100 where each electricalphase of the PCB stator 201 can be distributed in a plurality ofinterleaved PCB stators. In the example of FIG. 5, a three-phase PCBstator 201 is shown. The structures for each of the three phases can bedivided amongst three PCB panels each, in one embodiment. In thisversion, there is a total of nine PCB panels, including: panels 201 a 1,201 a 2 and 201 a 3 for phase A, panels 201 b 1, 201 b 2 and 201 b 3 forphase B, and panels 201 c 1, 201 c 2 and 201 c 3 for phase C. The statorpanels for each phase can be interleaved in, for example, a repeatingpattern to form three sets of three-panel stators, where each panel in aset is assigned to one of the three phases. In this example, panels201A1, 201B1 and 201C1 are for Set 1, panels 201A2, 201B2 and 201C2 arefor Set 2, and panels 201A3, 201B3 and 201C3 are for Set 3. The fluxlinked with each stator can vary across the stator structure, in thisembodiment. The average flux linkage in each phase, however, can be moreuniform than the example depicted in FIG. 4. As a result, the inducedvoltage per phase can be more balanced in FIG. 5.

FIG. 6 shows details of panels of the PCB stator 201 depicted in FIG. 5.Each PCB panel 201A1, 201B1 and 201C1 can have multiple layers. In theexample shown in FIG. 6, each stator panel has four layers 251. Eachlayer 251 can have a plurality of coils. The layers 251 can beinterconnected with buried vias 241. The layers 251 can be connected toother panels, to a power supply outside the device 100 or othercomponents with vias 261. Although FIGS. 5 and 6 show an example of athree-phase PCB stator with nine interleaved stator panels and eachpanel comprising four layers, other embodiments are possible includingdevices with different numbers of phases, different numbers of PCBpanels, and different numbers of layers. The number of layers in eachpanel can be the same or different. In some embodiments, the totalnumber of layers per phase can be adjusted to balance the voltageinduced in each phase.

FIG. 7A illustrate an example of an embodiment where the panel can havea first layer 251A where coils 210A can have a first number of turns(e.g., 3 turns), and a second layer 251B where coils 210B can havesecond number of turns different from the first number of turns (e.g., 2turns). Thus, the total number of turns per phase can be adjusted to,for example, balance the voltage induced in each phase. Otherembodiments can have different combinations of turns per coil.

Moreover, some embodiments as the one shown in FIG. 7B can have layers251 where a first set of coils 210A have a first number of turns (e.g.,3 turns) and a second set of coils 210B have a second number of turnsdifferent from the first number of turns (e.g., 2 turns), so the totalnumber of turns per phase can be further adjusted to balance the voltageinduced in each phase. The coil pattern shown in FIG. 7B can repeatthroughout the layer.

Other embodiments can have different patterns of coils and turns percoils (e.g., one coil with 4 turns and one coil with 5 turns, or twocoils with 4 turns and one coil with 3 turns).

Furthermore, some embodiments can have PCB panels with first and secondlayers. The first layer can have a first set of coils with a firstnumber of turns (e.g., 3 turns), and a second set of coils with a secondnumber of turns (e.g., 2 turns). Versions of the second layer can have athird set of coils with a third number of turns (e.g., 4 turns), and afourth set of coils with a fourth number of turns (e.g., 5 turns). Insome examples, the first, second, third and fourth number of turns canbe all different, all the same, of any permutation of values.

It should be understood that the embodiments described herein anddepicted in the drawings can be applicable to both PCB stators having asingle, integral, monolithic stator structure and to those having asegmented stator structure that is coupled together to form the PCBstator.

FIG. 8 shows a typical coil 210 formed on a PCB stator. Coil 210 caninclude multiple turns depending on the design of the PCB stator. FIG. 8depicts an example of a 3-turn coil in the PCB stator. Each turn caninclude two straight sections 220 of conductors that are substantiallyradially oriented with respect to the axis of the circular disk PCB. Thestraight sections 220 are connected by arches or arch segments 230 thatare circumferential relative to the axis.

A lesser desired effect of the interaction between the magnetic fieldestablished by magnets 130 and the stator conductors can include thegeneration of eddy currents in the straight sections 220. Eddy currentsare undesirable since they do not produce useful torque. In addition,they can generate losses that can produce heat and they can reduce theefficiency of the machine. Eddy currents are affected, among otherfactors, by the length of the conductor immersed in the magnetic field,as well as its angle relative to the direction of the relative motionbetween the coil and the magnetic field. In the example of FIG. 8, theangle 280 between the straight sections 220 and the tangential directionof motion 290 of the magnetic field is approximately 90 degrees. Theeddy current on a conductor can be proportional to the length of thestraight sections 220, and to the sine of the angle 280 between thestraight sections 220 and the direction of motion 290 of the magneticfield. The largest eddy currents can occur when the angle 280 is 90degrees.

FIG. 9 shows an alternate stator coil structure 300 where the typicallystraight radial conductors 220 (compare FIG. 8) in the active area 270of the magnetic field are configured as shorter conductor segmentsextending in different (e.g., alternating) directions. In the version ofFIG. 9, the conductors can be formed in a serrated pattern 310. Theserrated pattern can include linear or non-linear (e.g., arcuate)segments coupled together. The ‘radial’ conductors no longer provide astraight path for eddy currents. Instead, the radial portions of theconductors are configured in shorter conductor segments 310A and 310B.The absolute value of angles 320A and 320B relative to the direction ofmotion 290 of the magnets can be greater than 90 degrees, in someembodiments. This architecture can reduce eddy current losses in thesystem. In this example, the combined absolute value of angles 320A and320B is about 135 degrees. However, other angles greater than 90 degreescan be selected.

FIG. 10 shows an alternate embodiment of a non-linear coil structure 400where the typically straight radial conductors 220 (compare FIG. 8) areconfigured as conductors 410 with a generally ‘square wave’ pattern.This version can include a plurality of shorter conductor segments 410Athat can be substantially parallel to each other and can besubstantially perpendicular to the direction of motion 290 of themagnets. Alternate segments can be offset laterally from each other, asshown. Adjacent segments can be connected by a conductor segment 410Bthat can be oriented in a substantially circumferential or tangentialdirection (e.g., for circular disk embodiments), or in the same generaldirection of motion 290 of the magnets to form generally ‘square wave’patterns. In these embodiments, the ‘square wave’ pattern can reduceeddy current losses in the system.

Other embodiments can include conductors arranged in otherconfigurations. For example, versions of the conductors can be in asinusoidal or ‘sine wave’ pattern along a general radial direction.Still other patterns can include a ‘trapezoidal wave’ pattern, anotherpattern or a combination of the patterns described herein. The coils canhave multiple layers connected by blind or buried vias. Coils can bedistributed over any number of layers and connected in parallel, seriesor combinations thereof.

As the device 100, shown in FIGS. 1 and 2, is powered, electricalcurrents circulate through the coils 210 in the stator 200 (refer toFIG. 3A). The circulation of currents produces resistive losses, and theinteraction between the currents, external magnetic fields and themagnetic fields produced by the currents themselves produce eddy currentlosses. The combination of the resistive and eddy currents lossesgenerate heat in the PCB stator 200. This is an undesired effect of thecirculation of currents in the PCB stator 200 since it increases thetemperature of the stator. In extreme cases, the temperature rise of thePCB stator 200 may exceed the temperature class of the laminate used inthe PCB stator 200 leading to its premature failure. Accordingly, it isdesirable to remove heat from the PCB stator 200 to keep its temperaturebelow the temperature class of the PCB laminate material.

The mechanisms for removing heat from the PCB stator 200 can includeconduction, convection, and radiation heat transfer. FIG. 11 shows someof the heat removal mechanisms in the PCB stator 200. Some of the heatgenerated in the conductors of the coils 210 is carried by conduction205 to the external surfaces of the PCB stator 200 where it can beremoved by an air flow 215 provided by a fan or blower. Other portionsof the heat generated by the coils 210 can be carried by conduction 225along the layers of the PCB stator 200 toward the area where the PCBstator 200 is coupled to the machine housing 235 by means of fasteners245. The fasteners 245 can be screws, clamps, pins, etc., orcombinations thereof. Heat 255 can continue to be conducted through themachine housing 235 towards cooler surfaces and volumes as illustratedin FIG. 11.

These heat removal mechanisms can be hindered by the generally poorthermal conductivity of the PCB laminate material. For example, thethermal conductivity is typically about 0.3 W/mK perpendicular to thePCB plane, and about 0.9 W/mK in the PCB plane. If the surfacetemperature of the PCB is greater than the surrounding surfaces, some ofthe heat generated in the PCB can be radiated to the surroundingsurfaces. The net radiation heat transfer can be expressed by thefollowing Stefan-Boltzmann Law q=εσ(T_(h) ⁴−T_(c) ⁴)A, where q is theheat transfer, ε is the emissivity coefficient of the PCB, σ is theStefan-Boltzmann constant, T_(h) is temperature of the PCB, T_(c) is thetemperature of the surrounding surfaces, and A is the area of the PCB.Although existing heat transfer designs are workable, improvementscontinue to be of interest.

The embodiments disclosed herein can incorporate one or more thermallyconductive layers and features to the PCB. Such features can enhance theheat removal process and lower the overall temperature rise of the PCB.The addition of a layer of thermally conductive material (e.g., copper,anisotropic graphite or graphene, or combinations thereof) to one sideor both sides of the PCB, can form a low heat resistance path tofacilitate conductive heat flow from the PCB to the machine housing. Inaddition, the conductive layer(s) can act as a heat spreader to increaseconvection cooling of the PCB.

The embodiments described herein refer to ‘thermally conductive layers’and to ‘electrically conductive layers’. Versions of the thermalconductive layer can merely conduct heat and are not connected to anelectrical voltage or current source. Examples of electricallyconductive layers can be provided to conduct electric current via tracesor coils that can be coupled to a voltage or current source.

FIG. 12 shows a cross-section of an embodiment of a PCB stator 500 withfour electrically conductive layers 501. Each layer 501 can have aplurality of coils. In some versions, a layer of a thermally conductivematerial 510 can be included on both large surfaces of the PCB stator500. The PCB stator 500 can have an inner diameter edge 505 and an outerdiameter edge 530. The outer diameter edge 530 is typically the portionthat engages the machine housing 550 when the PCB stator 500 is mountedin the machine housing 550. The external thermally conductive layers 510can extend from the portion at or near the outer diameter edge 530 tothe portion at or near the inner diameter edge 505 of the PCB stator500.

In some embodiments, vias 540 can be added to the portion near the outeredge 530 of the PCB stator 500. Vias 540 can thermally connect theexternal thermally conductive layers 530, thereby facilitating heat flowbetween the two surfaces of the PCB stator 500. Although FIG. 12 showsvias 540 located at two radial locations, it should be understood thatother embodiments may not have any vias or may have vias 540 at only oneradial location, or at more than two radial locations connecting theexternal thermally conductive layers 510.

In some embodiments, alternative or additional vias 545 can be added tothe portion near the inner edge 505 of the PCB stator 500. Vias 545 alsocan facilitate heat flow between the two thermally conductive layers 510on the surfaces of the PCB stator 500. Although FIG. 11 shows vias 545located at one radial location, it should be understood that otherembodiments may not have any vias 545 or may have vias 545 located intwo or more radial locations connecting the external thermallyconductive layers 510.

In some embodiments, heat sinks formed from thermally conductivematerials (e.g., copper alloys, aluminum alloys, etc.) can be includedwith the PCB stator 500 to facilitate heat removal by convection. FIG.12 shows a version of heat sinks 515 that are attached, for example,with fasteners 525 to both large sides of the PCB stator 500. The heatsinks 515 can contact the thermally conductive layers 510 adjacent theinner diameter edge 505 of the PCB stator 500. The fasteners 525 can berivets, bolts and nuts, etc. The heatsinks 515 also can be soldered tothe thermally conductive layers 510. The heatsinks 515 can facilitateheat removal by the airflow 560 in the air gap 570 between the PCBstator 500 and the rotors 580.

FIG. 12 also depicts alternative or additional heat sinks 535 coupled toboth large sides of the PCB stator 500 near the outer diameter edge 530.The heat sinks 535 can contact the thermally conductive layers 510.Version of the heat sinks 535 can be coupled to the PCB stator 500 withfasteners 520, such as those described herein. In other embodiments, theheat sinks 535 can be coupled to the PCB stator 500 with dedicatedfasteners or with solder. Although FIG. 12 shows an embodiment with heatsinks adjacent both edges of the PCB stator, it should be understoodthat some embodiments may have heat sinks mounted only adjacent theinner edge or only adjacent the outer edge of the PCB stator.

Embodiments of the heatsinks 515 and 535 can be formed from a continuousstrip of thermally conductive material or can be segmented. FIG. 13shows the PCB stator 500 with heat sinks mounted to one of its externalthermally conductive layers 510. The heat sink 515 mounted adjacent theinner diameter edge of the PCB stator 500 can include at least twosegments 515A and 515B. The heat sink 535 mounted adjacent the outerdiameter edge of the PCB stator 500 can include at least two segments535A and 535B. Other embodiments can have heat sinks with more than twosegments.

Heat sinks can have profiles intended to enhance the heat transfer tothe cooling air. The heatsinks 515 and 535 shown in FIG. 13 can includerectangular fingers 516 and 536, respectively. Other embodiments canhave heat sinks with fingers with different shapes, such as trapezoidal,rhomboidal fingers, etc. The heatsink 515 shown in FIG. 13 can besubstantially flat. In contrast, the heat sink 535 has fingers 536 thatoriented out of plane relative to the body of the heat sink 535. Otherembodiments can include different configurations of heat sinks and/orfingers. As an example, a heat sink may have some of its fingersin-plane and other fingers out of plane. Still other heat sinks may havesome of the fingers at a first angle (e.g., 15 degrees) relative to theplane of the heat sink body, and other fingers oriented at a secondangle (e.g., 30 degrees), relative to the plane of the heat sink body.Alternative angles, shapes and combinations are possible.

The use of thermally conductive layers is not limited to the externalportions of the PCB stator. For example, FIG. 14 shows an embodimentwhere an internal thermally conductive layer 590 is included in the PCBstator 500. In this embodiment, the internal thermally conductive layer590 can extend from or adjacent the outer diameter edge 530 to oradjacent the inner diameter edge 505 of the PCB stator 500. It can bethermally connected to the external thermally conductive layers 510 withvias 540, 545, which are described herein.

Similar to the example shown in FIG. 12, the embodiment depicted in FIG.14 also includes heat sinks 515 and 535 coupled to the externalthermally conductive layers 510 with fasteners 525 and 520,respectively. Other embodiments may not have heatsinks or may haveheatsinks in only one edge of the PCB stator 500. Although theembodiment shown in FIG. 14 has one internal thermally conductive layerlocated approximately halfway between the two external surfaces of thePCB stator, it should be understood that other embodiments may have moreinternal thermally conductive layers in different structures andlocations.

FIGS. 15A and 15B illustrate PCB stators 500 with electricallyconductive layers 501, external thermally conductive layers 510, andinternal thermally conductive layers 590. FIG. 15A is an example of aPCB stator structure 500 with two evenly spaced internal thermallyconductive layers 590 spaced apart from each other by four electricallyconductive layers 501, and also respectively spaced apart by fourelectrically conductive layers 501 from the external thermallyconductive layers 510. FIG. 15B is an example of a PCB stator structure500 with three unevenly spaced, internal thermally conductive layers590. The internal thermally conductive layers 590 are spaced apart fromeach other by two electrically conductive layers 501, and alsorespectively spaced apart by four electrically conductive layers 501from the external thermally conductive layers 510.

Other arrangements of thermally and electrically conductive layers canbe used. Moreover, whereas some embodiments with multiple internalthermally conductive layers can include thermally connecting vias 540and 545 and heat sinks 515 and 545, other embodiments can include onlythermally connecting vias. All of these embodiments are applicable toboth monolithic PCB stators and those with a segmented structure coupledtogether to form the PCB stator.

Adding a thermally conductive layer 510 to the exterior of the PCBstator 500 can lower the emissivity of the PCB, thereby reducing theradiation heat transfer from the PCB. The emissivity of the heatconduction layer(s) can be increased through, for example, heat and/orchemical oxidation of the copper traces, and/or by adding a thin soldermask over the traces. By raising the emissivity, the radiation heattransfer from the PCB can be increased. Further, by increasing theemissivity of the surfaces surrounding the PCB, the radiation heattransfer from the PCB can be increased.

As thermally conductive materials tend to be good electrical conductors,and the thermally conductive layers are exposed to varying magneticfields that can induce unwanted eddy currents, it is desirable toprovide these layers with features that limit the circulation of eddycurrents.

FIG. 16 depicts an embodiment with a thermally conductive layer 510. Thethermally conductive layer 510 can include one or more substantiallystraight, radial, thermally conductive traces 610 extending from oradjacent the inner diameter edge 505 to or adjacent an outer diameteredge 530 of the PCB stator 500. FIG.16 shows the approximate location ofthe portion of the PCB that is subject to magnetic field variation. Thisalso is referred to as the active area 270 of the PCB stator 500. Inactive area 270, the traces 610 can be substantially thin to reduce eddycurrent losses in the thermally conductive layer. The trace width in thecircumferential or tangential direction can vary, for example, fromabout 0.005 inches to about 0.040 inches in some embodiments. Othersizes also can be used. The thickness of the traces 610 in the axialdirection can vary depending of the availability of PCB laminates. Forexample, the traces 610 can comprise copper at 1, 2 or 3 ounces persquare foot, or other thicknesses. The traces 610 can include thedesired PCB thermal characteristics.

In some versions, the traces 610 can merge to a continuous orsubstantially continuous portion or area 620 of thermally conductivematerial at or adjacent the outer diameter edge 530. Area 620 caninclude one or more vias to connect the thermally conductive layers inthe PCB. As described herein, some embodiments may not have vias. Thearea 620 of thermally conductive material also may include through holesto facilitate mounting the PCB stator to the machine housing.

Examples of the thermally conductive traces 610 can be coupled on onlyone end to prevent the circulation of eddy currents. FIG. 17 shows adetailed view of an embodiment of the thermally conductive layer shownin FIG. 16 where the ends 615 of the traces 610 at or adjacent the innerdiameter edge 505 are not interconnected.

Other embodiments of the thermally conductive traces may have anon-linear layout, such as that shown in FIG. 18. Examples of the traces630 can include a serrated pattern. Similarly to the embodiment depictedin FIG. 16, the traces 630 can be coupled by a continuous orsubstantially continuous component 620 of thermally conductive materialat or adjacent the outer diameter edge 530 of the PCB stator 500. Someversions of the traces 630 are not coupled at or adjacent the innerdiameter edge 505 (FIG. 19), such that the ends 635 of the traces 630are not interconnected.

Examples of one or more of the external thermally conductive layers 510depicted in FIGS. 12 through 19 can be galvanically connected to themachine housing 550. Accordingly, the external thermally conductivelayers 510 can provide an electrical grounding plane for the PCB stator500. Such configurations can prevent the occurrence of corona dischargeon the surfaces of the PCB stator 500. For example, these embodimentscan be useful in applications where the PCB stator 500 operates at avoltage that corona discharge could occur if the grounding plane was notprovided.

Whereas the examples depicted in FIGS. 16 and 18 depict externalthermally conductive layers with various trace patterns, it should beunderstood that internal conductive layers can also comprise thermallyconductive traces with various trace patterns.

Other embodiments can have substantially continuous areas of thermallyconductive material near the inner and the outer edges of the statorPCB, to enable, as an example, the installation of heat sinks, aspreviously shown in FIGS. 12 and 13. The embodiment depicted in FIGS. 20and 21 is an example of a PCB stator where the thermally conductivelayer 510 has a continuous or substantially continuous thermallyconductive material area 640 near the inner edge 505, and a continuousor substantially continuous thermally conductive material area 620 nearthe outer edge 530. In these versions, the thermally conductive materialareas 620 and 640 can establish a circulation path for eddy currentsinduced in the traces 630 of the thermally conductive layer 510. Toprevent the circulation of eddy currents in the thermally conductivelayer 510, the traces 630 can be interrupted, such as the discontinuity650 shown.

Although FIGS. 20 and 21 show the location of the discontinuity 650 atabout one-third of the length of the trace 630 from the inner edge 505,other embodiments may have the discontinuity in other locations, such asin the mid-point of the traces 630.

It should be understood that, whereas the embodiment depicted in FIGS.20 and 21 have the thermally conductive layer traces in a serratedpattern, other embodiments may have straight traces or some otherpattern. Moreover, the pattern and features described herein can also bepresent in internal thermally conductive layers and are also applicableto stator PCBs comprised of a single annular stator structure orcomprised of segmented annular stator structure.

FIGS. 22A and 22B show an embodiment of heat conductive layers where twoadjacent traces 660 are connected at the end 670 adjacent the inner edge505 of the PCB stator, and connected to two separate leads 680A and680B, respectively, adjacent the outer edge 530 of the PCB stator. Theleads 680A, 680B can be connected to a motor monitoring system that canmeasure the voltage induced on their respective traces 660 duringoperation. A plurality of such pairs of traces 660 can be included onone or both faces of the PCB stator.

These embodiments can serve to detect if the rotor contacts the statorduring operation. In the event of rotor-stator contact, such as due to amechanical malfunction, the friction between the rotor and the heatconductive traces 660 can grind off one or more of the traces 660,including those coupled to the motor monitoring system. If such an eventoccurs, the voltage measured by the motor monitoring system coming fromthe affected traces 660 can drop to a zero value or substantially closeto a zero value, which can trigger a motor shut down and/or a warning tothe system operator before there is catastrophic damage to the stator orother parts of the machine.

Although FIGS. 22A and 22B illustrate an embodiment of a rotor-statorcontact detector in a heat conductive layer with linear traces, the samearrangement can be achieved in a heat conductive layer with non-lineartraces, such as the other embodiments described herein.

FIGS. 23A and 23B depict an embodiment where the PCB stator 500 can beclamped between two interlocking sections 550A and 550B of the housing550. In this embodiment, the stator 500 can have heat sinks 535sandwiched between each of the two major sides of the PCB stator 500 andthe respective housing sections 550A, 550B. Furthermore, the PCB stator500 can have a plurality of mounting holes 710, which can be oblong inshape. In some examples, the mounting holes 710 can substantiallyradially align (relative to the axis of rotation) with and receivealignment pins 720. The alignment pins 720 can position and secure thePCB stator 500, housing sections 550A, 550B and heat sinks 535proximately centered with the axis of rotation of the device.

In some embodiments, the alignment pins 720 can be press fit to at leastone of the housing sections 550A, 550B. The alignment pins 720 can havea sliding fit with the mounting holes 710 since, in some versions, themounting holes 710 are elongated. This can be useful when the PCB stator500 thermally expands during operation. The diameter of the PCB stator500 can slide and grow into the circumferential gap 730 between thestator perimeter edge 530 and interior of the housing 550.

Although FIGS. 23A and 23B show an embodiment where heat sinks 535 arepresent on both major sides of the PCB stator 500, other embodiments canhave heat sinks on only one side or have no heat sinks at all.Furthermore, although the example shown has alignment pins 720 in allmounting holes 710, other embodiments can have alignment pins 710 inonly some of mounting holes 710.

Other embodiments can include one or more of the following items.

1. An axial field rotary energy device, comprising:

rotors having an axis of rotation, and each rotor comprises a magnet;and

a stator assembly located axially between the rotors and configured tooperate a plurality of electrical phases, the stator assembly comprisesa plurality of printed circuit board (PCB) panels, each PCB panelcomprises a plurality of layers, each PCB panel is designated to one ofthe electrical phases, each electrical phase of the stator assembly isconfigured to be provided by a plurality of the PCB panels, and the PCBpanels for each electrical phase are axially spaced apart from andintermingled with each other.

2. The device wherein the PCB panels for each electrical phase areuniformly axially interleaved with each other in a repeating pattern.

3. The device wherein every PCB panel comprises a same number of layers.

4. The device wherein a first layer in at least one of the PCB panelscomprises coils with a first number of turns, and a second layercomprises coils with a second number of turns that differs from thefirst number of turns.

5. The device wherein a first layer in at least one of the PCB panelscomprises both coils with a first number of turns and coils with asecond number of turns that differs from the first number of turns.

6. The device wherein at least one of the PCB panels comprises adifferent numbers of layers than another PCB panel.

7. The device wherein a first layer in at least one of the PCB panelscomprises coils with a first number of turns, and a second layercomprises coils with a second number of turns that differs from thefirst number of turns.

8. The device wherein a first layer in a selected PCB panel comprisesboth coils with a first number of turns and coils with a second numberof turns that differs from the first number of turns.

9. The device wherein a second layer said at least one of the PCB panelscomprises both coils with a third number of turns and coils with afourth number of turns that differs from the third number of turns.

10. The device wherein a second layer in the selected PCB panelscomprises both coils with a third number of turns and coils with afourth number of turns that differs from the third number of turns.

11. The device wherein the stator assembly comprises discrete, PCBradial segments that are mechanically and electrically coupled togetherto form the stator assembly.

12. The device wherein the PCB panels for each electrical phase areuniformly axially interleaved with each other in a repeating pattern.

13. The device wherein every PCB panel comprises a same number oflayers.

14. The device wherein a first layer in at least one of the PCB panelscomprises coils with a first number of turns, and a second layercomprises coils with a second number of turns that differs from thefirst number of turns.

15. The device wherein a first layer in at least one of the PCB panelscomprises both coils with a first number of turns and coils with asecond number of turns that differs from the first number of turns.

16. The device wherein at least one of the PCB panels comprises adifferent numbers of layers than another PCB panel.

17. The device wherein a first layer in at least one of the PCB panelscomprises coils with a first number of turns, and a second layercomprises coils with a second number of turns that differs from thefirst number of turns.

18. The device wherein a first layer in a selected PCB panel comprisesboth coils with a first number of turns and coils with a second numberof turns that differs from the first number of turns.

19. The device wherein a second layer said at least one of the PCBpanels comprises both coils with a third number of turns and coils witha fourth number of turns that differs from the third number of turns.

20. The device wherein a second layer in the selected PCB panelscomprises both coils with a third number of turns and coils with afourth number of turns that differs from the third number of turns.

1. An axial field rotary energy device, comprising:

rotors having an axis of rotation, and each rotor comprises a magnet;and

a stator assembly located axially between the rotors, the statorassembly comprises a plurality of printed circuit board (PCB) panels,each PCB panel comprises a plurality of layers and each layer comprisesa plurality of coils, each coil comprises radial traces relative to theaxis, the radial traces comprise non-linear radial traces coupled byarch traces that are transverse to the non-linear radial traces.

2. The device wherein the non-linear radial traces comprise a serratedpattern.

3. The device wherein an absolute value of an angle between portionsthat form the non-linear radial traces, relative to a direction ofmotion of the rotors, is greater than 90 degrees.

4. The device wherein the non-linear radial traces comprise a squarewave pattern.

5. The device wherein the non-linear radial traces comprise a sine wavepattern.

6. The device wherein the stator assembly comprises discrete PCBsegments.

7. The device wherein the non-linear radial traces comprise a regularrepeating pattern.

8. The device wherein the non-linear radial traces comprise an irregularrepeating pattern.

9. An axial field rotary energy device, comprising:

rotors having an axis of rotation, and each rotor comprises a magnet;

a stator assembly located axially between the rotors, the statorassembly comprises a plurality of printed circuit board (PCB) panels,each PCB panel comprises a plurality of layers and each layer comprisesa plurality of coils, each coil comprises radial traces relative to theaxis, the radial traces comprise non-linear radial traces coupled byarch traces that are transverse to the non-linear radial traces; andwherein

the stator assembly comprises discrete, PCB radial segments that aremechanically and electrically coupled together to form the statorassembly.

10. The device wherein the non-linear radial traces comprise a serratedpattern.

11. The device wherein an absolute value of an angle between portionsthat form the non-linear radial traces, relative to a direction ofmotion of the rotors, is greater than 90 degrees.

12. The device wherein the non-linear radial traces comprise a squarewave pattern.

13. The device wherein the non-linear radial traces comprise a sine wavepattern.

14. The device wherein the non-linear radial traces comprise a regularrepeating pattern.

15. The device wherein the non-linear radial traces comprise anirregular repeating pattern.

16. An axial field rotary energy device, comprising:

rotors having an axis of rotation, and each rotor comprises a magnet;and

a stator assembly located axially between the rotors, the statorassembly comprises a plurality of printed circuit board (PCB) panels,each PCB panel comprises a plurality of layers and each layer comprisesa plurality of coils, each coil comprises radial traces relative to theaxis, the radial traces comprise non-linear radial traces coupled byarch traces that are transverse to the non-linear radial traces;

the non-linear radial traces comprise a serrated pattern; and

an absolute value of an angle between portions that form the serratedpattern, relative to a direction of motion of the rotors, is greaterthan 90 degrees.

17. The device wherein the stator assembly comprises discrete, PCBradial segments that are mechanically and electrically coupled togetherto form the stator assembly.

1a. An axial field rotary energy device, comprising:

rotors having an axis of rotation, and each rotor comprises a magnet;and

a stator assembly located axially between the rotors, the statorassembly comprises a plurality of printed circuit board (PCB) panels,each PCB panel comprises a plurality of layers, each layer comprises aplurality of coils, and at least one outer portion of the statorassembly comprises an external thermally conductive layer that extendsfrom an inner diameter portion to an outer diameter portion of thestator assembly.

1b. An axial field rotary energy device, comprising:

rotors having an axis of rotation, and each rotor comprises a magnet;

a stator assembly located axially between the rotors, the statorassembly comprises a plurality of printed circuit board (PCB) panels,each PCB panel comprises a plurality of layers, each layer comprises aplurality of coils, and at least one outer portion of the statorassembly comprises an external thermally conductive layer that extendsfrom an inner diameter portion to an outer diameter portion of thestator assembly; and

each PCB panel comprises discrete, PCB radial segments that aremechanically and electrically coupled together to form the respectivePCB panels.

2. The device wherein both major outer sides of the stator assemblycomprise respective external thermally conductive layers that arethermally coupled to each other.

3. The device wherein the external thermally conductive layers arethermally coupled with a plurality of vias.

4. The device wherein at least one surface of each external thermallyconductive layer comprises a treatment to increase emissivity thereof.

5. The device wherein the vias are located adjacent the inner and outerdiameter portions.

6. The device further comprising heat sinks comprising thermallyconductive material coupled adjacent at least one of the inner and outerdiameter portions.

7. The device wherein each heat sink comprises discrete heat sinksegments.

8. The device wherein each heat sink comprises fingers that extend froma plane of the heat sink.

9. The device wherein some of the fingers are oriented at a first angleand other ones of the fingers are oriented at a second angle thatdiffers from the first angle.

10. The device further comprising an internal thermally conductive layerlocated inside the stator assembly.

11. The device wherein the internal thermally conductive layer isthermally coupled to the external thermally conductive layer with vias.

12. The device wherein the vias are located adjacent at least one of theinner and outer diameter portions.

13. The device further comprising heat sinks comprising thermallyconductive material coupled adjacent to at least one of the inner andouter diameter portions.

14. The device wherein each heat sink comprises discrete heat sinksegments.

15. The device wherein each heat sink comprises fingers that extend froma plane of the heat sink.

16. The device wherein some of the fingers are oriented at a first angleand other ones of the fingers are oriented at a second angle thatdiffers from the first angle.

17. The device further comprising a plurality of internal thermallyconductive layers.

18. The device wherein the internal thermally conductive layers areevenly spaced apart from each other.

19. The device wherein the internal thermally conductive layers areunevenly spaced apart from each other.

20. The device wherein the thermally conductive layers comprise radialthermal traces that are thermally coupled at ends thereof adjacent theouter diameter portion with a continuous thermal coupler.

21. The device wherein the continuous thermal coupler comprises aninternal continuous thermal coupler.

22. The device wherein the continuous thermal coupler comprises anexternal continuous thermal coupler.

23. The device wherein the continuous thermal coupler comprises internaland external continuous thermal couplers.

24. The device wherein the internal and external continuous thermalcouplers are thermally coupled together with vias that are thermallyconductive.

25. The device wherein the radial thermal traces comprise a linearpattern.

26. The device wherein the radial thermal traces comprise a non-linearpattern.

27. The device wherein the radial thermal traces comprise a serratedpattern.

28. The device wherein the radial thermal traces comprisediscontinuities that disrupt circulation of eddy currents.

29. The device wherein the radial thermal traces are thermally coupledat ends thereof adjacent the inner diameter portion with a continuousthermal coupler.

30. The device wherein the thermally conductive traces have a non-linearpattern.

31. The device wherein the thermally conductive traces have a serratedpattern.

32. The device where at least one pair of radial thermal traces is notconnected to any thermal couplers, and the at least one pair of radialthermal traces is connected adjacent the inner diameter portion of thestator assembly and are further connected to a voltage sensor of a motormonitoring system.

33. The device wherein the external thermally conductive layers aregalvanically coupled to a machine housing of the device and configuredto provide electrical grounding for the stator assembly.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. The terms “comprises,” “comprising,” “including,” and“having,” are inclusive and therefore specify the presence of statedfeatures, integers, steps, operations, elements, and/or components, butdo not preclude the presence or addition of one or more other features,integers, steps, operations, elements, components, and/or groupsthereof. The method steps, processes, and operations described hereinare not to be construed as necessarily requiring their performance inthe particular order discussed or illustrated, unless specificallyidentified as an order of performance. It is also to be understood thatadditional or alternative steps may be employed.

When an element or layer is referred to as being “on,” “engaged to,”“connected to,” or “coupled to” another element or layer, it may bedirectly on, engaged, connected or coupled to the other element orlayer, or intervening elements or layers may be present. In contrast,when an element is referred to as being “directly on,” “directly engagedto,” “directly connected to,” or “directly coupled to” another elementor layer, there may be no intervening elements or layers present. Otherwords used to describe the relationship between elements should beinterpreted in a like fashion (e.g., “between” versus “directlybetween,” “adjacent” versus “directly adjacent,” etc.). As used herein,the term “and/or” includes any and all combinations of one or more ofthe associated listed items.

Although the terms first, second, third, etc. may be used herein todescribe various elements, components, regions, layers and/or sections,these elements, components, regions, layers and/or sections should notbe limited by these terms. These terms may be only used to distinguishone element, component, region, layer or section from another region,layer or section. Terms such as “first,” “second,” and other numericalterms when used herein do not imply a sequence or order unless clearlyindicated by the context. Thus, a first element, component, region,layer or section discussed below could be termed a second element,component, region, layer or section without departing from the teachingsof the example embodiments.

Spatially relative terms, such as “inner,” “outer,” “beneath,” “below,”“lower,” “above,” “upper,” “top”, “bottom,” and the like, may be usedherein for ease of description to describe one element's or feature'srelationship to another element(s) or feature(s) as illustrated in thefigures. Spatially relative terms may be intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the example term “below” can encompass both anorientation of above and below. The device may be otherwise oriented(rotated degrees or at other orientations) and the spatially relativedescriptions used herein interpreted accordingly.

This written description uses examples to disclose the embodiments,including the best mode, and also to enable those of ordinary skill inthe art to make and use the invention. The patentable scope is definedby the claims, and can include other examples that occur to thoseskilled in the art. Such other examples are intended to be within thescope of the claims if they have structural elements that do not differfrom the literal language of the claims, or if they include equivalentstructural elements with insubstantial differences from the literallanguages of the claims.

In the foregoing specification, the concepts have been described withreference to specific embodiments. However, one of ordinary skill in theart appreciates that various modifications and changes can be madewithout departing from the scope of the invention as set forth in theclaims below. Accordingly, the specification and figures are to beregarded in an illustrative rather than a restrictive sense, and allsuch modifications are intended to be included within the scope ofinvention.

It can be advantageous to set forth definitions of certain words andphrases used throughout this patent document. The term “communicate,” aswell as derivatives thereof, encompasses both direct and indirectcommunication. The terms “include” and “comprise,” as well asderivatives thereof, mean inclusion without limitation. The term “or” isinclusive, meaning and/or. The phrase “associated with,” as well asderivatives thereof, can mean to include, be included within,interconnect with, contain, be contained within, connect to or with,couple to or with, be communicable with, cooperate with, interleave,juxtapose, be proximate to, be bound to or with, have, have a propertyof, have a relationship to or with, or the like. The phrase “at leastone of,” when used with a list of items, means that differentcombinations of one or more of the listed items can be used, and onlyone item in the list can be needed. For example, “at least one of: A, B,and C” includes any of the following combinations: A, B, C, A and B, Aand C, B and C, and A and B and C.

Moreover, various functions described herein can be implemented orsupported by one or more computer programs, each of which is formed fromcomputer readable program code and embodied in a computer readablemedium. The terms “application” and “program” refer to one or morecomputer programs, software components, sets of instructions,procedures, functions, objects, classes, instances, related data, or aportion thereof adapted for implementation in a suitable computerreadable program code. The phrase “computer readable program code”includes any type of computer code, including source code, object code,and executable code. The phrase “computer readable medium” includes anytype of medium capable of being accessed by a computer, such as readonly memory (ROM), random access memory (RAM), a hard disk drive, acompact disc (CD), a digital video disc (DVD), solid state drive (SSD),or any other type of memory. A “non-transitory” computer readable mediumexcludes wired, wireless, optical, or other communication links thattransport transitory electrical or other signals. A non-transitorycomputer readable medium includes media where data can be permanentlystored and media where data can be stored and later overwritten, such asa rewritable optical disc or an erasable memory device.

Also, the use of “a” or “an” is employed to describe elements andcomponents described herein. This is done merely for convenience and togive a general sense of the scope of the invention. This descriptionshould be read to include one or at least one and the singular alsoincludes the plural unless it states otherwise.

The description in the present application should not be read asimplying that any particular element, step, or function is an essentialor critical element that must be included in the claim scope. The scopeof patented subject matter is defined only by the allowed claims.Moreover, none of the claims invokes 35 U.S.C. § 112(f) with respect toany of the appended claims or claim elements unless the exact words“means for” or “step for” are explicitly used in the particular claim,followed by a participle phrase identifying a function.

Benefits, other advantages, and solutions to problems have beendescribed above with regard to specific embodiments. However, thebenefits, advantages, solutions to problems, and any feature(s) that cancause any benefit, advantage, or solution to occur or become morepronounced are not to be construed as a critical, required, sacrosanctor an essential feature of any or all the claims.

After reading the specification, skilled artisans will appreciate thatcertain features which are, for clarity, described herein in the contextof separate embodiments, can also be provided in combination in a singleembodiment. Conversely, various features that are, for brevity,described in the context of a single embodiment, can also be providedseparately or in any subcombination. Further, references to valuesstated in ranges include each and every value within that range.

What is claimed is:
 1. An axial field rotary energy device, comprising:rotors having an axis of rotation, and each rotor comprises a magnet; astator assembly located axially between the rotors, the stator assemblycomprises a plurality of printed circuit board (PCB) panels, each PCBpanel comprises a plurality of layers, each layer comprises a pluralityof coils, and at least one outer portion of the stator assemblycomprises an external thermally conductive layer that extends from aninner diameter portion to an outer diameter portion of the statorassembly; both major outer sides of the stator assembly compriserespective external thermally conductive layers that comprise radialthermal traces that are thermally coupled to each other; and wherein theexternal thermally conductive layers are galvanically coupled to amachine housing of the device and configured to provide electricalgrounding for the stator assembly.
 2. The device of claim 1, wherein atleast some of the radial thermal traces comprise discontinuities thatcan disrupt circulation of eddy currents.
 3. An axial field rotaryenergy device, comprising: rotors having an axis of rotation, and eachrotor comprises a magnet; and a stator assembly located axially betweenthe rotors, the stator assembly comprises a plurality of printed circuitboard (PCB) panels, each PCB panel comprises a plurality of electricallyconductive layers, each electrically conductive layer comprises aplurality of coils, and at least one outer portion of the statorassembly comprises an external thermally conductive layer that isseparate from the electrically conductive layers and extendscontinuously in a radial direction from an inner diameter portion to anouter diameter portion of the stator assembly.
 4. The device of claim 3,wherein both major outer sides of the stator assembly compriserespective external thermally conductive layers that are thermallycoupled to each other.
 5. The device of claim 4, wherein the externalthermally conductive layers are thermally coupled with a plurality ofvias.
 6. The device of claim 2, wherein the thermally conductive traceshave a non-linear pattern.
 7. The device of claim 2, wherein thethermally conductive traces have a serrated pattern.
 8. The device ofclaim 5, wherein the vias are located adjacent the inner and outerdiameter portions.
 9. The device of claim 4, wherein at least onesurface of each external thermally conductive layer comprises atreatment to increase emissivity thereof.
 10. The device of claim 3,further comprising heat sinks comprising thermally conductive materialcoupled adjacent at least one of the inner and outer diameter portions.11. The device of claim 10, wherein each heat sink comprises discreteheat sink segments.
 12. The device of claim 10, wherein each heat sinkcomprises fingers that extend from a plane of the heat sink.
 13. Thedevice of claim 12, wherein some of the fingers are oriented at a firstangle and other ones of the fingers are oriented at a second angle thatdiffers from the first angle.
 14. The device of claim 3, furthercomprising an internal thermally conductive layer located inside thestator assembly.
 15. The device of claim 14, wherein the internalthermally conductive layer is thermally coupled to the externalthermally conductive layer with vias.
 16. The device of claim 15,wherein the vias are located adjacent at least one of the inner andouter diameter portions.
 17. The device of claim 14, further comprisingheat sinks comprising thermally conductive material coupled adjacent toat least one of the inner and outer diameter portions.
 18. The device ofclaim 17, wherein each heat sink comprises discrete heat sink segments.19. The device of claim 18, wherein each heat sink comprises fingersthat extend from a plane of the heat sink.
 20. The device of claim 19,wherein some of the fingers are oriented at a first angle and other onesof the fingers are oriented at a second angle that differs from thefirst angle.
 21. The device of claim 3, further comprising a pluralityof internal thermally conductive layers.
 22. The device of claim 21,wherein the internal thermally conductive layers are evenly spaced apartfrom each other.
 23. The device of claim 21, wherein the internalthermally conductive layers are unevenly spaced apart from each other.24. The device of claim 3, wherein the external thermally conductivelayer comprises radial thermal traces that are thermally coupled at endsthereof to a substantially continuous area of thermally conductivematerial adjacent to an outer edge of the PCB.
 25. The device of claim24, wherein the substantially continuous area of thermally conductivematerial is adjacent to an inner edge of the PCB.
 26. The device ofclaim 24, further comprising a second substantially continuous area ofthermally conductive material adjacent to an inner edge of the PCB. 27.The device of claim 26, wherein the external thermally conductive layeris thermally coupled to a second external thermally conductive layerwith vias that are thermally conductive.
 28. The device of claim 24,wherein the external thermally conductive layer comprises radial thermaltraces that comprise a linear pattern.
 29. The device of claim 24,wherein the external thermally conductive layer comprises radial thermaltraces that comprise a non-linear pattern.
 30. The device of claim 24,wherein the external thermally conductive layer comprises radial thermaltraces that comprise a serrated pattern.
 31. The device of claim 24,wherein at least one pair of the radial thermal traces is not connectedto any other thermal traces or substantially continuous area ofthermally conductive material, and the at least one pair of radialthermal traces is connected adjacent to the inner diameter portion ofthe stator assembly and is further connected to a voltage sensor of amotor monitoring system.